The invention relates to optical fiber light transmission. More specifically, the invention relates to orienting a light source and an optical fiber for optical fiber light transmission.
Fiber optics is a branch of physics based on the transmission of light through transparent fibers. Individual or bundled optical fibers, each having a diameter measuring less than 0.00015 inch, can carry light for hundreds of miles. An optical fiber has a highly transparent core, typically constructed from glass or plastic and encased in a cladding. Light from a laser, incandescent light bulb or other source enters one end of the optical fiber. Light traveling through the core is contained by the cladding because the inside surface of the cladding bends or reflects light inwardly. At the other end of the fiber, a detector, such as a photosensitive device or the human eye, receives the light.
Optical fibers (including lensed fibers, graded index fibers and thermally expanded core fibers, among others, with or without integrated or otherwise associated optical elements) may be single- or multi-mode. Conventionally, single-mode fibers are used for long-distance transmissions.
A fiber has a core having an aperture with an acceptance angle. Referring to FIG. 1, an acceptance angle 26 is an angular measurement between opposed asymptotes 30 extending from an edge 23 of an aperture 22. Rotating the asymptotes 30 about the sight line 24 of the aperture 22 defines a conically-extending view field. From the perspective of the aperture 22, at a distance 34 from the aperture 22, the view field 32 appears as shown in dashed lines. Light 20 thrown from a light source 36 outside of a view field is not received in the aperture 22. View field size is a function of aperture size.
A small view field necessitates precise connections between a fiber and light source, other fibers in the system and any detector. Thus, fibers typically are coupled with a precision light source, such as laser light emitter. A lens L or curved mirror (not shown) sometimes is used to focus light on the aperture A of a fiber F, as shown in FIG. 2. However, these intervening light guides negatively impact on overall transmission efficiency. The added parts and assembly also undesirably increase the cost and timing required for coupling the light source and the optical fiber.
Often, single- and/or multi-mode fibers are bundled proximate to a light source and convey light received to diverse locations. In such cases, the light source and optical fibers must be oriented so that each fiber aperture receives a desired amount of light.
Finally, light sources often have anisotropic light throwing characteristics. For example, an incandescent light source, as shown in FIG. 3, may include a filament 42 formed into a coil 44 having an axis 46. The coil 44 projects a singular, ring-shaped projection having a particular luminescence, as viewed in the axial direction 48, or a series of rod shapes having a different luminescence, as viewed in the orthogonal direction 50. The light source projects optimal luminescence along an optimal projection line between the axial and orthogonal directions. Orienting the light source so that it projects optimal luminescence toward an optical fiber aperture yields optimal performance from the optical fiber.
The foregoing demonstrates a need for an apparatus and method for orienting any light source and any individual or bundle of optical fibers so that the light source projects optimal luminescence toward desired optical fiber apertures.
The invention is an apparatus and method for coupling a light source with individual or bundled, single- or multi-mode optical fibers. The invention eliminates the need for lenses and mirrors to focus light on an optical fiber aperture. Thus, the invention eliminates costly parts and assembly operations otherwise required. The invention also eliminates efficiency losses occasioned when a medium, such as a lens, is used to reflect or refract light towards the optical fiber. Further, the invention provides for obtaining optimal luminescence from an anisotropically-luminescent spatially incoherent light source.
An exposed portion of each optical fiber core forms an aperture with a sight line and an acceptance angle that defines a view field. Light thrown by a light source positioned outside of the view field is not received in the aperture. The invention orients a light source and individual or bundled optical fibers so that the light source is within a view field.
The invention also orients individual or bundled optical fibers and a light source with anisotropic light-throwing characteristics so that the light source projects an optimal projection toward an aperture for optimal luminescence.
These and other features of the invention will be appreciated more readily in view of the drawings and detailed description below.